additional disassembly on life-src
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nino-porcino
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272601bc18
commit
fd59a6c934
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@ -2,11 +2,9 @@
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; UNKNOWN AUTHOR
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; DISASSEMBLED BY ANTONINO PORCINO, 14TH SEP 2022
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ECHO = $FFEF ; character echo routine in woz monitor
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ECHO = $FFEF ; character echo routine in Woz monitor
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KEY_DATA = $D010 ; read key
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KEY_CTRL = $D011 ; control port
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DSP_DATA = $D012 ; write ascii
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DSP_CTRL = $D013 ; control port
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; zero page variables
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@ -17,9 +15,18 @@ PTR4 = $F8 ; $F8-$F9
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CELLCOUNT = $F9 ; also PTR4 high byte
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RND = $FA ; $FA-$FB random seed
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;
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; board geometry is 40x24 = 960 bytes
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; there are two boards stored in memory:
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; primary board: $2440-$27FF
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; secondary board: $2840-$2BFF
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;
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; the boards contains the actual characters that are printed on
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; the screen: live cell ("*"), dead cell (" ") and top/bottom border ("-")
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;
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BOARD = $2440
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BOARDEND = $2800
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ROW0 = $2440
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ROW1 = $2468
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@ -30,11 +37,11 @@ DEADCELL = $A0 ; " " (space character)
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ALIVECELL = $AA ; "*"
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FRAMECELL = $AD ; "-"
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ORG $2000
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;
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; quickly resets the primary board ($2400-$27FF)
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; clears the primary board ($2400-$27FF)
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; bug: the area between $2400-$243F is cleared as well
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;
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LDX #$00
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LDA #DEADCELL ; dead cell character
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@ -46,106 +53,128 @@ L2004 STA $2400,X ; bug: this should be $2440
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BNE L2004
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;
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; prints welcome message (56 characters)
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; X is zero from previous BNE
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; prints the welcome message (56 characters)
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; (X is zero from previous BNE)
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;
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L2013 LDA MESSAGE,X
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JSR ECHO
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INX
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CPX #$38 ; prints 56 chars
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CPX #56 ; prints 56 characters of the message
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BNE L2013
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; read and print string from keyboard until ENTER is pressed
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; string is simply discarded, the purpose is to increment the
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; random seed in $FA-RND+1
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;
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; read and print from keyboard until ENTER is pressed
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; typed characters are simply discarded, the purpose
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; is to increment the random seed in $FA-FB (RND variable)
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;
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L201E JSR RDKEY
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CMP #$8D ; enter key
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BNE L201E
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;
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; fills the board with a random number of cells (from 32 to 95)
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; bug: also fills out of screen area between $2400 and $243F
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; fills the board with a random number of live cells (from 32 to 95)
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; bug: also writes out of the screen area between $2400 and $243F
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;
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JSR GETRAND ; gets a random number
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JSR GETRAND ; gets a random number (0-255) in A
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AND #$3F ; ranges it $00-$3F
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ADC #$20 ; ranges it $20-$5F (TODO: why carry is not cleared?)
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STA CELLCOUNT ; number of cells to write betwen $20-$5F (32-95)
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ADC #$20 ; ranges it $20-$5F (why carry is not cleared?)
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STA CELLCOUNT ; number of cells to generate betwen $20-$5F (32-95)
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LDY #$00
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L2030 JSR GETRAND ; gets a random number
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LDY #$00 ; keeps Y to 0 for "STA(),Y" instruction
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L2030 JSR GETRAND ; gets a random number in A
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AND #$03 ; ranges it 0-3
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CLC
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ADC #$24
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STA PTR1+1 ; high byte ranges from $24-$27
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LDA RND
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STA PTR1 ; PTR1 points randomly $2400-$27FF
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ADC #BOARD/256 ; board high byte ($24)
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STA PTR1+1 ; high byte now ranges from $24-$27
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LDA RND ; get random number directly from seed
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STA PTR1 ; PTR1 now points randomly to $2400-$27FF
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LDA #ALIVECELL ; alive cell character ("*")
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STA (PTR1),Y ; set cell "ON"
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DEC CELLCOUNT ; decrement cell count
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DEC CELLCOUNT ; decrement cell counter
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BNE L2030 ; loop until all cells are written
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;
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;$2046
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; main game loop
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MAINLOOP LDA #$24
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STA PTR4+1
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LDA #$40
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STA PTR4 ; PTR4 = $2440
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;
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MAINLOOP LDA #BOARD/256 ;
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STA PTR4+1 ;
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LDA #BOARD%256 ;
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STA PTR4 ; sets PTR4 to $2440
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;
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; marks top and bottom lines of the board to avoid out of bound checks
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;
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LDX #$27 ; $27=39, counts 40 characters backward
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LDA #FRAMECELL ; $AD = board limit character ("-")
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L2052 STA $27D8,X ; write bottom line of the board
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STA $2440,X ; write top line of the board
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DEX ; decrement 40 charc counter
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LDX #39 ; counts 40 characters backward
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LDA #FRAMECELL ; board frame character ("-")
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L2052 STA ROW23,X ; write bottom line of the board
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STA ROW0 ,X ; write top line of the board
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DEX ; decrement char counter
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BPL L2052 ; loop if X >= 0
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; loop that prints the whole board from $2440 to $2800
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;
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; prints the whole board from $2440 to $2800
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; Y is already zero from above
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;
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L205B LDA (PTR4),Y
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JSR ECHO
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INC PTR4
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BNE L205B
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INC PTR4+1
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LDA PTR4+1
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CMP #$28
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CMP #BOARDEND/256
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BNE L205B
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;
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; reads the keyboard between each screen printout
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;
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JSR RDKEY
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; copy true board into "working" board (copies $2440-$2800 into $2840-...)
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;
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; copy primary board into secondary board (copies $2440-$27FF into $2840-$2BFF)
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;
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LDY #$00
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JSR SETPTRS ; PTR1=$2440, PTR2=$2840
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L2074 LDA (PTR1),Y
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STA (PTR2),Y
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JSR SETPTRS ; set board pointers: PTR1=$2440 (primary), PTR2=$2840 (secondary)
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L2074 LDA (PTR1),Y ; read from primary
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STA (PTR2),Y ; write into secondary
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INC PTR1
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INC PTR2
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BNE L2074
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INC PTR1+1
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INC PTR2+1
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LDA PTR1+1
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CMP #$28
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CMP #BOARDEND/256 ; check end of the board
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BNE L2074
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JSR ZEROBOARD ; fills the primary board all with zeros
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;
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; once the primary board is copied, it's used to count the number of
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; nearby cells around a live cell, so it's all set to 0
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;
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JSR ZEROBOARD
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;
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; scans the secondary board does some computation and writes on the primary board
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; scans the secondary board: for every live cell increment by one
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; the nearby cells in the primary board
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;
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; nearby cells are scanned using Y-indexing with the following Y values:
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;
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; -41 -40 -39
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; -1 * +1
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; 39 40 41
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;
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L208B LDY #$00
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LDA (PTR2),Y
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LDA (PTR2),Y ; read cell in the secondary board
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CMP #ALIVECELL ; is cell alive?
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BNE L209D ; if no go next cell
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LDY #$27 ; yes it's alive
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JSR L2114 ; ??
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LDY #$01
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JSR L211D ; ??
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LDY #39 ; yes it's alive, start Y indexing from 39
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JSR SUM6CELLS ; sum cells with Y offsets: +/-39, +/-40, +/-41 (row above and below the live cell)
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LDY #1
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JSR SUMYCELLS ; sum cells with Y offsets: +/-1 (left/right of live cell)
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; increment PTR1 and PTR2 to next cell
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L209D INC PTR1
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@ -154,47 +183,56 @@ L209D INC PTR1
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INC PTR1+1
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INC PTR2+1
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LDA PTR1+1
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CMP #$28 ; check end of the board
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CMP #BOARDEND/256 ; check end of the board
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BNE L208B
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;
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; ??? does something with top and bottom rows of the board
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; sums the score from bottom row into top, and top into bottom
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; this "wraps" the playfield making it like a toroid (sort of)
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;
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; ROW1 = ROW1 + ROW23
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; ROW22 = ROW22 + ROW0
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; why??
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;
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CLC
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LDX #$27 ; count 40 characters (1 row)
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LDX #39 ; count 40 characters (1 row)
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L20B0 LDA ROW23,X
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ADC ROW1,X
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STA ROW1,X
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LDA ROW0,X
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ADC ROW22,X
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ADC ROW22,X ; (due to low score, carry it's always zero, no need to CLC)
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STA ROW22,X
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DEX
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BPL L20B0
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JSR SETPTRS
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;
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; the actual GAME OF LIFE computation (Conway's rules)
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; here secondary buffer contains the old board ("*" or " ")
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; and primary buffer contains the number of nearby cells for each cell that is alive
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;
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JSR SETPTRS ; start from top of the boards
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L20C8 LDY #$00
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LDA (PTR1),Y
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CMP #$02 ; ? two cells around
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BNE L20D4
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LDA (PTR2),Y
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BNE L20DE
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L20D4 CMP #$03 ; ? three cells around
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BNE L20DC
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LDA #ALIVECELL ; set next cell alive
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CMP #2 ; two cells nearby?
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BNE L20D4 ; if not checks for three
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LDA (PTR2),Y ; yes two cells around: it survives to next round
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BNE L20DE
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L20D4 CMP #3 ; three cells nearby?
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BNE L20DC ; if not then it's dead cell
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LDA #ALIVECELL ; else it's alive (does not matter if it was alive or not)
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BNE L20DE ; anything else is dead cell
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L20DC LDA #DEADCELL ; set next cell dead
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L20DE STA (PTR1),Y
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L20DE STA (PTR1),Y ; write the cell on the board
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INC PTR1
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INC PTR2
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BNE L20C8
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INC PTR1+1
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INC PTR2+1
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LDA PTR2+1
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CMP #$2C
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CMP #$2C ; check end of the secondary board (ends at $2C00)
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BNE L20C8
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JMP MAINLOOP
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; set pointers to:
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@ -224,15 +262,14 @@ L2108 LDA KEY_CTRL
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JSR ECHO
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RTS
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; ???
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L2114 JSR L211D
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; $2114
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SUM6CELLS JSR SUMYCELLS
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INY
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CPY #$2A
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BNE L2114
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BNE SUM6CELLS
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RTS
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L211D ; increment cell at (PTR1),Y
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;$211D
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SUMYCELLS ; increment cell at (PTR1),Y
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CLC
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LDA (PTR1),Y
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ADC #$01
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@ -293,9 +330,9 @@ L2167 STA (PTR1),Y
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BNE L2167
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INC PTR1+1
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LDX PTR1+1
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CPX #$28 ; check end of the board
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CPX #BOARDEND/256 ; check end of the board
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BNE L2167
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JSR SETPTRS ; reset correct pointers on exit
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JSR SETPTRS ; reset correct pointers on exit
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RTS
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L2179:
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